Widespread service disruptions were reported on the A, B, C, D and F lines as a result of the derailment.

A southbound A train struck a tunnel wall after "the emergency brakes automatically went on," MTA Chairman Joe Lhota told reporters. "The train bucked forward, it bucked backward. In the process of doing that, two of the - there's eight cars on this train - two of the cars derailed."

Investigators are trying to determine why the emergency brakes were activated.

Passengers reported a door being ripped off one of the derailed cars. Broken glass flew inside. Firefighters helped about 500 riders riders climb down ladders onto the the tracks, and then helped them up a ladder onto the subway platform.

"It started rocking all over the place. People started falling off their chairs. It was crazy, like a movie," rider Edgar Gonzalez told WCBS-TV.